Most copper tubing used in air conditioning and refrigeration work is known as ACR tubing. This designation indicates that the tubing is intended for air conditioning and refrigeration and that it has been processed to give the desired characteristics. ACR tubing is charged with gaseous nitrogen to keep out air and eliminate oxidation when soldering and silver brazing fittings to the tubing. This tubing should have the ends plugged immediately after cutting a length from the piece.
Another type of copper tubing used in heating and plumbing is called nominal size tubing.
Copper tubing is available in both soft and hard types. Both hard and soft copper tubing is available in two wall thicknesses, K and L. Most ACR tubing used at present is the L thickness.